Hi and welcome to FixYa,
Peltier devices although not that efficient are known to be reliable. On your described problem, possibilities are:
- thermoelectric (Peltier) module(s) (most likely) - the active cooling elements. Most design have several sub-modules connected in series to form an array. Failure of one in between will fail the entire module;
- controller board (likely) - or more specifically the section that regulates/control supplied power to the Peltier modules;
- sensor (least likely) - most designs would have a sensor for the hotside forced ventilation system. If the external ventialtion (fan) fails, then the controller board would prevent supply of voltage to the modules;
- connectors (a possibility) - other than the Peltier effect, it is possible to have electrolysis on the terminals/connectors which would cause corrosion. Check and clean all connectors to expose fresh metal, ensure tightness and positive contact.
An easy check is to test for the presence / absence of voltage to the module(s). If voltage could be found, then it would be the Peltier module(s) that have failed. Absence of supply voltage would indicate the controller board to be possibly faulty. To confirm, determine if there is power supplied to the controller board but none is in turn supplied to the Peltier modules. Absence of power going into the controller board would indicate a power supply problem.
Please exercise due caution when working with a live unit.
Good luck and thank you for asking FixYa.